Johann Georg III (1647-1691) was Elector of the old German State of Saxony from 1680 to 1691. This coin is a 1/12 thaler. It is one of many, many coins minted in Saxony in all sorts of sizes, denominations, and patterns. The Standard Catalog for 1600-1700 has 36 large-size pages of Saxony coins, each coin listed by denomination, date, mint mark, and condition. Here is what it says for this coin:

The coin in our picture is in amazing condition. It looks fully uncirculated. Coin House SESAM Basel has it on sale for 80 euros, a really good price. As always, CoinQuest thanks Coin House SESAM Basel for use of their coin photo.